With the discussion that happened Saturday night, about her being sorry. It is posssible there is something she wants to tell you, but is scared as to what your reaction will be. Do not approach her or ask her outright if she has done anything, it will make her withdraw.
She seems to be taking on an awful lot at once, going back to school, job search, friends wedding, ect. It sounds like she is overleading herself and it is starting to form into depression (especially with the suicidal thoughts). Have you asked her if she is open to seeing a concellor for herself?
I know that there is something she wants to tell me. She has made the comment in the past that there is something that she needs to tell me but she couldn't do it at that time. Plus with the things that I found out (snooping) and her going to visit this guy and lying to me about it, I am pretty certain what it is. For sure, she was emotionally attached to this guy. I wouldn't be surprised if something physical happened also.
While she has yet to admit to anything, I found it surprising that she told me that her trip to see him was horrible and that she was so glad to get back home. I never asked about her vacation to visit "this friend". Yet she made it a point to tell me that he pissed her off pretty bad and she was so happy to get out of there and get back home. I guess the grass isn't always greener on the other side.
As for not saying anything to her and pressuring her....I know she is going to have a VERY hard time coming clean with me. I thought maybe if I said something to reassure her that it is ok to tell me that it might make her more comfortable. All I was going to say was, "You have stated that there is something you need to tell me but you seem afraid to do so. I just wanted you to know that I am hear for you and that you can tell me anything. You just might be surprised how understanding and forgiving people can be." And I was going to leave it at that.
In the past I have asked her to see a counselor because she has some problems she needs to deal with. Her coping skills are not the best, her father passing away when she was a young girl still bothers her, past abusive relationships, her insecurities with herself, etc. However, I never really pressed the issue on her seeing someone.
I did mention her seeing someone again when we broke up. I phrased it like so, "I am going to go see someone myself because I have some problems that I need to address. As a friend, I feel it would be good for you to see someone also....not for us, but for you." Her response was, "I am way too busy and I don't have the time." I responded, "It is only one hour every week or two. You have time to spend an hour going tanning everyday, you can make time for this." I have gone to see someone because there were things I could have done differently and I want to make myself a better person. However, I am pretty certain that she hasn't gone to see anyone yet. BTW, she doesn't know I have been going to talk to someone.